Biodegradable plastics are of increasing industrial interest as replacements or supplements for non-biodegradable plastics in a wide range of applications and in particular for packaging applications. One class of biodegradable polymers is the polyhydroxyalkanoates (PHAs), which are linear, aliphatic polyesters that can be produced by numerous microorganisms for use as intracellular storage material. Articles made from the polymers are generally recognized by soil microbes as a food source. There has therefore been a great deal of interest in the commercial development of these polymers, particularly for disposable consumer items. The polymers exhibit good biodegradability and useful physical properties.
Molecular weight, molecular weight distribution, and long chain branching are the dominating factors influencing processing and key physical properties of any polymeric composition.
PHA polymers have quite limited thermal stability, and undergo chain scission by beta-elimination mechanisms at general processing temperatures and conditions. This can reduce the molecular weight quite significantly which is undesirable for certain applications. Commercial utility of PHAs also can be limited in some applications, such as films, coatings and thermoforming, because of the low melt strength or melt elasticity often found in linear polymers. Thus, a need exists to address these shortcomings.